In-Situ NDE of Navy Sonar Domes Via X-Ray Backscatter Tomography

X-ray backscatter tomography (XBT) is a relatively new NDE technology which is quantitative in its ability to detect a flaw location in three dimensions. The volume to be inspected is interrogated by a collimated x-ray beam and one or more collimated detectors to measure the Compton scatter signal produced by each volume element. XBT is particularly useful where access is available only to one side of the object. Although a number of novel backscatter inspection techniques have been demonstrated [1–4], there is a notable dearth of real applications. This can be attributed to both the development of other, lower cost, one-sided methods and the lack, until recently, of a commercial XBT scanner. In applications where the low cost alternatives are inferior or unfeasible and failure costs are high, XBT affords a solution

A Practical Algorithm for Reconstruction From X-Ray Backscatter Data

Although numerous applications of x-ray backscatter tomography (XBT) have been demonstrated, only a few have been fully developed to practical implementation [1–5]. In some applications the images produced by direct data acquisition and display methods are plagued with superposition artifacts that can interfere with interpretation [6]. Non-homogeneous materials such as composites or layered structures are particularly susceptible. Reconstruction methods have been proposed to correct the datum from each volume element (voxel) by exploiting the information in data from overlying voxels [7]. Practical inspection systems, however, present a more challenging problem than the monoenergetic highly collimated laboratory demonstration systems. In particular, the use of a bremmstrahlung source and a fan beam, or slit collimated, detector geometry, deprives us of knowledge of the backscattered photon energies and paths that are needed for a true reconstruction. In this paper, we present our work towards a reconstruction using data from a commercial XBT system (Philips ComScan) and a real composite inspection application. Our approach uses pre-processing to remove system artifacts, a priori information about the material, and an iterative method to determine the composition of each voxel.</p

One Sided Radiographic Inspection Using Backscatter Imaging

Radiographic inspection, where access is limited to one side of the part, can be performed by the use of backscatter imaging techniques. Compton scattering is the primary source of the backscattered signal strength with some contribution from x-ray fluorescence. A variety of approaches have been used in both medicine and industry to create the images [1–25]. The flying spot technique which uses a collimated beam of x-rays, and a large area detector has been used in the work reported here. The backscatter imaging is particular useful in the inspection of low-density, composite materials.</p

Removal of power-line interference from the ECG: a review of the subtraction procedure

BACKGROUND: Modern biomedical amplifiers have a very high common mode rejection ratio. Nevertheless, recordings are often contaminated by residual power-line interference. Traditional analogue and digital filters are known to suppress ECG components near to the power-line frequency. Different types of digital notch filters are widely used despite their inherent contradiction: tolerable signal distortion needs a narrow frequency band, which leads to ineffective filtering in cases of larger frequency deviation of the interference. Adaptive filtering introduces unacceptable transient response time, especially after steep and large QRS complexes. Other available techniques such as Fourier transform do not work in real time. The subtraction procedure is found to cope better with this problem. METHOD: The subtraction procedure was developed some two decades ago, and almost totally eliminates power-line interference from the ECG signal. This procedure does not affect the signal frequency components around the interfering frequency. Digital filtering is applied on linear segments of the signal to remove the interference components. These interference components are stored and further subtracted from the signal wherever non-linear segments are encountered. RESULTS: Modifications of the subtraction procedure have been used in thousands of ECG instruments and computer-aided systems. Other work has extended this procedure to almost all possible cases of sampling rate and interference frequency variation. Improved structure of the on-line procedure has worked successfully regardless of the multiplicity between the sampling rate and the interference frequency. Such flexibility is due to the use of specific filter modules. CONCLUSION: The subtraction procedure has largely proved advantageous over other methods for power-line interference cancellation in ECG signals